Electrical connectors and adapters are used in a wide variety of applications in industry, and differ in shape, size and characteristics depending upon the types of service in which they are employed. In instances where wiring for emergency or backup systems are involved, electrical connectors cannot be employed with any reasonable expectation of reliability under the harsh conditions accompanying the emergency or back-up condition in which it must provide electrical service. This is because the use of the emergency or backup system will occur under conditions so extreme that the use of a standard service connector would cause failure. In these instances an adapter is utilized with the electrical conductors passing un-interrupted through the adapter.
This is especially so where the adapter is directly exposed to the hazardous condition. In the case of an aircraft firewall, the insulated side of the adapter may be exposed to physical contact from debris, as well as extremes in pressure and temperature. When the firewall is adjacent an engine compartment, it can be expected that the temperatures can quickly rise to high levels, that the pressure on the adapter can build, and that debris may strike the adapter.
The emergency and backup electrical services which typically extend into an engine compartment include the engine fire extinguisher actuator and possibly the engine thrust reversing actuators. The purpose of the adapter is to keep the wires undamaged and insulated at the point where they extend across the boundary and into the high temperature area. Since the adapter is designed for emergency and back-up systems, it must function to keep the conductors in-tact under the particular emergency conditions for which the emergency equipment will be needed.
Another consideration for an adapter is the degree to which the cold side of the firewall is isolated from hot gasses. Even if the adapter does not fail in the sense that the conductors do not fail, a failure which allows hot, perhaps toxic fumes to leave the containment area on the hot side of the firewall is unacceptable. Many adapters are designed to protect the integrity of the wires passing therethrough without regard to truly isolating and sealing the area on the hot side of the firewall.
To insure that a given adapter will withstand such emergency conditions, a test has been devised which an adapter must pass to be found acceptable for emergency service. The test subjects the adapter to a temperature of 2000.degree. Fahrenheit for 15 minutes. The test is performed by using a burner which is lit and allowed to achieve the 2000.degree. Fahrenheit temperature measured by the flame heating of a thermocouple. As soon as the 2000.degree. temperature is attained, the burner is placed in front of the adapter at a distance of four inches from the adapter, and elapsed time is recorded while the adapter is observed for failure.
For example, one such adapter utilized a back plate on the reverse side of a firewall along with a nextel ceramic fiber gasket on the "hot" side of the firewall, followed by an inconel plate, a cylindrical, soft silicone insert, a ceramic insulator plate abutting the end of the cylindrical soft insulator, and finally a cylindrical inconel weldment surrounding the soft silicone and ceramic insulator plate. The inconel weldment consisted of a plate portion welded to a cylindrical portion which was welded to a ring. The plate portion of the inconel weldment was bolted to the inconel plate located on the back side or "cold" side of the firewall.
This configuration was only able to with stand three minutes of the 2000.degree. Fahrenheit flame test. Further, this failing configuration, not including bolts and washers, required eight pieces of hardware and significant labor involved in welding the inconel weldment. This configuration also carried the conductors in a horizontal row, as did the inconel plate on the cold side of the firewall, the ceramic fiber gasket, the inconel plate on the hot side of the firewall and the silicone and ceramic insulators. The conductors were lined up horizontally across the circular cross section of the silicone insulator and were therefore not evenly spaced with respect to other conductors or the edges of the adapter.
Since adapters are used in bulk numbers and in a variety of services, their performance and resources required for production and installation are an important aspect of their use and acceptance. A single aircraft may require hundreds of such adapters of various sizes to adequately protect the various back-up and emergency systems of the aircraft. Aside from the resources required for production, the labor resources required for installation and replacement also represent a major resource expenditure. The time required to assemble even one less piece of hardware is significant when considering the multiplier effect arising from the use of hundreds and thousands of the adapters over the course of time.
What is therefore needed is an adapter having a number of salient characteristics which improve its performance and reduce the resources expended to achieve such performance. The ideal adapter should have a lesser number of parts, will be amenable to more simplified manufacture, and be made of superior materials. The ideal adapter will be easy to install quickly and will be completely serviceable. Further, the ideal adapter will not only pass, but exceed the 2000.degree. Fahrenheit flame test outlined above and provide a complete seal off of the hot side of a firewall. Such sealing should especially be accomplished about the insulated conductors to prevent degradation of the insulation to the maximum extent practicable under emergency conditions.